Fix various problems with GS4QueryHandler

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/GS4QueryHandler.java

@@ -9,6 +9,7 @@ import com.google.common.collect.ImmutableSet;
 import com.velocitypowered.api.event.query.ProxyQueryEvent;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.plugin.PluginContainer;
+import com.velocitypowered.api.plugin.PluginDescription;
 import com.velocitypowered.api.proxy.Player;
 import com.velocitypowered.api.proxy.server.QueryResponse;
 import com.velocitypowered.proxy.VelocityServer;
@@ -19,6 +20,7 @@ import io.netty.channel.socket.DatagramPacket;
 import java.net.InetAddress;
 import java.nio.charset.StandardCharsets;
 import java.security.SecureRandom;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
@@ -33,8 +35,6 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
 public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket> {
 
-  private static final Logger logger = LogManager.getLogger(GS4QueryHandler.class);
-
   private static final short QUERY_MAGIC_FIRST = 0xFE;
   private static final short QUERY_MAGIC_SECOND = 0xFD;
   private static final byte QUERY_TYPE_HANDSHAKE = 0x09;
@@ -59,10 +59,6 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
       .expireAfterWrite(30, TimeUnit.SECONDS)
       .build();
   private final SecureRandom random;
-
-  private volatile @MonotonicNonNull List<QueryResponse.PluginInformation> pluginInformationList
-      = null;
-
   private final VelocityServer server;
 
   public GS4QueryHandler(VelocityServer server) {
@@ -93,15 +89,10 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
     ByteBuf queryMessage = msg.content();
     InetAddress senderAddress = msg.sender().getAddress();
 
-    // Allocate buffer for response
-    ByteBuf queryResponse = ctx.alloc().buffer();
-    DatagramPacket responsePacket = new DatagramPacket(queryResponse, msg.sender());
-
-    try {
     // Verify query packet magic
     if (queryMessage.readUnsignedByte() != QUERY_MAGIC_FIRST
         || queryMessage.readUnsignedByte() != QUERY_MAGIC_SECOND) {
-        throw new IllegalStateException("Invalid query packet magic");
+      return;
     }
 
     // Read packet header
@@ -115,9 +106,12 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
         sessions.put(senderAddress, challengeToken);
 
         // Respond with challenge token
+        ByteBuf queryResponse = ctx.alloc().buffer();
         queryResponse.writeByte(QUERY_TYPE_HANDSHAKE);
         queryResponse.writeInt(sessionId);
         writeString(queryResponse, Integer.toString(challengeToken));
+
+        DatagramPacket responsePacket = new DatagramPacket(queryResponse, msg.sender());
         ctx.writeAndFlush(responsePacket, ctx.voidPromise());
         break;
       }
@@ -127,24 +121,24 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
         int challengeToken = queryMessage.readInt();
         Integer session = sessions.getIfPresent(senderAddress);
         if (session == null || session != challengeToken) {
-            throw new IllegalStateException("Invalid challenge token");
+          return;
         }
 
         // Check which query response client expects
         if (queryMessage.readableBytes() != 0 && queryMessage.readableBytes() != 4) {
-            throw new IllegalStateException("Invalid query packet");
+          return;
         }
 
-          // Build query response
+        // Build initial query response
         QueryResponse response = createInitialResponse();
-
+        boolean isBasic = queryMessage.isReadable();
-          boolean isBasic = queryMessage.readableBytes() == 0;
 
         // Call event and write response
         server.getEventManager()
             .fire(new ProxyQueryEvent(isBasic ? BASIC : FULL, senderAddress, response))
             .whenCompleteAsync((event, exc) -> {
               // Packet header
+              ByteBuf queryResponse = ctx.alloc().buffer();
               queryResponse.writeByte(QUERY_TYPE_STAT);
               queryResponse.writeInt(sessionId);
 
@@ -169,19 +163,13 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
               }
 
               // Send the response
+              DatagramPacket responsePacket = new DatagramPacket(queryResponse, msg.sender());
               ctx.writeAndFlush(responsePacket, ctx.voidPromise());
             }, ctx.channel().eventLoop());
-
         break;
       }
       default:
-          throw new IllegalStateException("Invalid query type: " + type);
+        // Invalid query type - just don't respond
-      }
-    } catch (Exception e) {
-      logger.warn("Error while trying to handle a query packet from {}", msg.sender(), e);
-      // NB: Only need to explicitly release upon exception, writing the response out will decrement
-      // the reference count.
-      responsePacket.release();
     }
   }
 
@@ -191,20 +179,13 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
   }
 
   private List<QueryResponse.PluginInformation> getRealPluginInformation() {
-    // Effective Java, Third Edition; Item 83: Use lazy initialization judiciously
+    List<QueryResponse.PluginInformation> result = new ArrayList<>();
-    List<QueryResponse.PluginInformation> res = pluginInformationList;
+    for (PluginContainer plugin : server.getPluginManager().getPlugins()) {
-    if (res == null) {
+      PluginDescription description = plugin.getDescription();
-      synchronized (this) {
+      result.add(QueryResponse.PluginInformation.of(description.getName()
-        if (pluginInformationList == null) {
+          .orElse(description.getId()), description.getVersion().orElse(null)));
-          pluginInformationList = res = server.getPluginManager().getPlugins().stream()
-              .map(PluginContainer::getDescription)
-              .map(desc -> QueryResponse.PluginInformation
-                  .of(desc.getName().orElse(desc.getId()), desc.getVersion().orElse(null)))
-              .collect(Collectors.toList());
     }
-      }
+    return result;
-    }
-    return res;
   }
 
   private static class ResponseWriter {